Nylon foam

ABSTRACT

A nylon foam product produced by frothing in an intensive mixer a reaction mixture of catalyst, caprolactam and polyol prepolymer in the presence of a surfactant and gaseous frothing agent.

BACKGROUND OF THE INVENTION

This invention relates to nylon foams and a method of producing same, inparticular, it relates to a foam produced by means of the mechanicalfrothing of a nylon block copolymer material.

Nylon 6 block copolymers (NBC) are a class of polymers based on theanionic polymerization of caprolactam with polymeric polyols. Ingeneral, the system utilizes di-functional imides which act as couplingagents between polyol and nylon blocks, as well as functioning asactivated sites for caprolactam polymerization.

In the procedure of Nylon 6 block copolymers, two reactant streams arebrought together, mixed and finally injected under pressure into a moldwherein polymerization and development of resin properties areessentially achieved. The first of the two reactant streams comprise acatalyst dissolved in molten caprolactam, and the second comprises aprepolymer of a polyol reacted with a bisimide in molten caprolactam.

The NBC system so produced may be modified in a number of ways and findexcessive use in reaction injection molding operation, in that such asystem yields products generally characterized by a good impactstrength/stiffness balance and a relatively flat modular temperatureresponse.

SUMMARY OF THE INVENTION

This invention comprises a nylon block copolymer foam having a densityof from about 10 lbs/ft³ to about 60 lbs/ft³ wherein said foam productis produced by frothing the resultant mixture of two modifiedcaprolactam streams in the presence of a surfactant and a frothingagent. Specifically, the process for producing said foam is as follows:

(a) A stream of molten caprolactam that is catalyzed with caprolactammagnesium bromide is intensively mixed with a molten caprolactam streamthat is modified with a prepolymer of a polyol and a bisimide;

(b) While mixing said streams, in an intensive mixer, a siliconesurfactant and a frothing agent are combined therewith;

(c) The reactant mixture is injected into heated molds where it isallowed to cure; and,

(d) The resultant product that is removed from the molds is a toughrigid structural foam having a uniform cell size and a density of from10 to 60 lbs/ft³.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram generally identifying the method of producingthe NBC foam of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As seen in FIG. 1 of the drawings, the first part of the processinvolves the preparation of two reactant streams which are ultimatelymixed in an intensive mixture.

The first of such reactant streams is noted as A-Catalyst and representsa catalyzed caprolactam. Typically, a bromide catalyst is added tomolten caprolactam in which it reacts and dissolves. Said catalystscomprise from about 5% to 25% by weight of the reaction mixture.

The second reactant stream designated in the drawing as B-Polyolbasically comprises a polyol and a bisimide coupler-activator alsodissolved in molten caprolactam in stoichiometric portions so as toensure polymerization. In the uncatalyzed state, i.e., before mixed withreactant stream A, reactant stream B is a stable mixture for anindefinite period of time. Typically, a polyol such as polypropyleneglycol is combined with bis acyllactam to form the prepolymer and fromabout 10% to 90% by weight of said prepolymer is combined with themolten caprolactam. The acyllactam end groups act as an initiator forthe caprolactam polymerization which results in a block copolymercomprised of polyether soft segments and nylon 6 hard segments.

While maintaining each reactant stream at about 70° C. to 90° so as toprevent degradation, the two reactant streams are pumped to an intensivemixer where they are combined with from 2% to about 10% of a surfactantin the presence of an inert gas, such as nitrogen. Such surfactant ispreferably a silicone based product; however, any surfactant which iscompatible with the system may be used. It has been found that varyingthe flow rate of the gas to the intensive mixer during frothing allowscontrol of the density of the foam product of from about 10 lbs/ft³ toabout 60 lbs/ft³.

Once the two reactant streams have been mixed for a sufficient period oftime and the surfactant and frothing agent have been added thereto, theresultant liquid is injected into a preheated mold where it is allowedto cure into a solid nylon foam product of a uniform cell size.

The following examples are provided to further illustrate the scope ofthe present invention; however, they should not be considered to belimiting thereof.

In the following example, a catalyzed reactant stream, Stream A,comprises 1,000 grams to caprolactam and 250 grams Nyrim catalyst (acaprolactam magnesium bromide catalyst manufactured by Monsanto Company)and polyol stream, Stream B, comprises 600 grams caprolactam and 400grams Nyrim Prepolymer (a prepolymer of bis acyllactam reactant with ahydroxyl terminated polypropylene oxide polymer sold by MonsantoCompany). In each case, the surfactant employed was Niax 5614 (a blockcopolymer of polydimethysiloxane and polyoxyalkylene available fromUnion Carbide Corporation), a silicone-based surfactant, and thefrothing agent was nitrogen gas introduced to the mixture via aRotameter so as to give selected froth densities.

    ______________________________________                                                       EXAMPLES                                                       Conditions       1      2      3     4    5                                   ______________________________________                                        Stream A Temperature (°F.)                                                              190    195    180   170  170                                 Stream B Temperature (°F.)                                                              190    200    205   165  165                                 Stream A Flow (g/min)                                                                          91.1   70     71    33.5 53                                  Stream B Flow (g/min)                                                                          91.1   70     81    33.5 53                                  Surfactant Flow (g/min)                                                                        10     9      0     9    9                                   Mixing Speed (RPM)                                                                             600    600    1100+ 1100 1100                                Froth Density (lb/ft.sup.3)                                                                    25     55     --    43   53                                  Mold Temperature (°F)                                                                   275    275    275   280  270                                 Cure Time (Min)  5      5      5     5    5                                   Foam Density (lb/ft.sup.3)                                                                     20     52.2   --    40   54                                  ______________________________________                                    

As will be noted from the above examples, the density of the final foamproduct is controlled by the amount of inert gas injected (as measuredby froth density). All final molded foam products were tough and rigidwith uniform cell size.

It will be clear to those skilled in the art that the same techniques asdisclosed herein could be used to make liquid cast nylon foam whichcontains no soft segment blocks. Also, soft segment blocks other thanpolyether, such as polybutadiene, could be employed to make theprepolymer.

Having thus described this invention, what is claimed is:
 1. A processfor preparing a nylon block copolymer foam comprising:(a) mixing acatalyzed reactant stream comprising a bromide catalyst dissolved inmolten caprolactam with a second molten caprolactam stream containing apolyol prepolymer prepared by reacting a polyol with bis acyllactam inan intensive mixer; (b) adding a silicone-based surfactant and afrothing agent to said mixture so as to froth the mixture; (c) injectingsaid frothed mixture into a preheated mold, and (d) curing said frothedmixture in said mold to form said foam.
 2. The process of claim 1wherein said surfactant comprises between 2% and 10% by volume of saidmixture in said mixer.
 3. The process of claim 1 wherein said frothingagent is an inert gas.
 4. The process of claim 1 wherein said foam has adensity of from about 10 lbs/ft³ to about 60 lbs/ft³ in its cured state.